[yocto] Getting linker -l into a bbappend

[colin.helliwell at ln-systems.com]

I have an autotools (C++) app which builds fine with my default recipe. But
for a particular platform an additional (C) library is needed, so I have a
bbappend.
I can add in the additional compiler flag here, but I'm struggling to
specify the additional library linkage - I think it's because the ordering
on the linker command line is wrong.

If I add '-lfoo' to the base Makefile.am then it builds fine (though
strangely, "-lfoo" isn't anywhere in the linker command line?). 
But I'm trying to put this into just the 'append' rather than altering the
base [non-platform-specific] Makefile.

I've tried 
    EXTRA_OEMAKE += " LDFLAGS+="-lfoo" " 
and
    LDFLAGS+="-lrfctrl"
but these don't seem to construct the correct linkage order (functions from
the library are undefined references)

Is there a way to append this in the right way?
Thanks